Scooter uses a small size Puppia harness. We have been through 3 levels of obedience classes and it works great. It is easy on and easy off. I have not tried Chattiesmom's harness but a lot of members like them. I bought the Puppia harness in the beginning (two years ago) and it is still working well. He started as an X-Small and now uses the Small. I only use it for walks or training class, otherwise he has a regular collar, so that may be why it has lasted us so long. Puppia harnesses are super soft and adjustable so you can adjust the body size as necessary.
Here is a link to the kind Scooter has:
Puppia Dog Harness Soft Mesh